Axiomatic approach to radiation reaction of scalar point particles in curved spacetime

Several different methods have recently been proposed for calculating the motion of a point particle coupled to a linearized gravitational field on a curved background. These proposals are motivated by the hope that the point particle system will accurately model certain astrophysical systems which are promising candidates for observation by the new generation of gravitational wave detectors. Because of its mathematical simplicity, the analogous system consisting of a point particle coupled to a scalar field provides a useful context in which to investigate these proposed methods. In this paper, we generalize the axiomatic approach of Quinn and Wald in order to produce a general expression for the self force on a point particle coupled to a scalar field following an arbitrary trajectory on a curved background. Our equation includes the leading order effects of the particle's own fields, commonly referred to as ``self force'' or ``radiation reaction'' effects. We then explore the equations of motion which follow from this expression in the absence of non-scalar forces.Comment: 17 pages, 1 figur

Neutrino Fluxes from Active Galaxies: a Model-Independent Analysis

There are tantalizing hints that jets, powered by supermassive black holes at the center of active galaxies, are true cosmic proton accelerators. They produce photons of TeV energy, possible higher, and may be the enigmatic source of the highest energy cosmic rays. Photoproduction of neutral pions by accelerated protons on UV light is the source of the highest energy photons, in which most of the bolometric luminosity of the galaxy may be emitted. The case that proton beams power active galaxies is, however, far from conclusive. Neutrinos from the decay of charged pions represent an uncontrovertible signature for the proton induced cascades. We show that their flux can be estimated by model-independent methods, based on dimensional analysis and textbook particle physics. Our calculations also demonstrate why different models for the proton blazar yield very similar results for the neutrino flux, consistent with the ones obtained here.Comment: Latex 2.09 with epsf.sty. 12 pages, 2 postscript figures. Compressed postscript version of paper with figures also available soon at http://phenom.physics.wisc.edu/pub/preprints/1997/madph-97-982.ps.Z or at ftp://phenom.physics.wisc.edu/pub/preprints/1997/madph-97-982.ps.

The speaking vocabulary of grade two

Thesis (M.A.)--Boston Universit

Positive distraction for children during burn wound care in Australia — An evaluation of the ‘Captains on Call’ pilot

Introduction: Burn wound care procedures can cause severe pain to the child, and distress for both the child and caregivers. We evaluated a new Starlight Children's Foundation program, ‘Captains on Call’, which aims to provide positive distraction during burn wound care procedures to reduce the child's anxiety and pain. This paper presents a preliminary evaluation, using a qualitative design, of Captains on Call at the Women's and Children's Hospital, Australia. Methods: We conducted interviews with caregivers (n = 18), patients (n = 6), nurses (n = 5) and Captain Starlights (n = 3). Interviews focused on program impact and recommendations for how to improve the program. Results: We identified seven themes: (1) positive distraction from pain and boredom, (2) benefit of additional support, (3) creating positive memories of the hospital, (4) catering for unique needs of each patient and family, (5) general appreciation, (6) importance of regular visits, and (7) a desire to expand the program. All caregivers, nurses and patients reported that they were likely to recommend the program to others. Conclusion: This study provides early evidence to support the benefit of the Captains on Call program to families and health professionals, as well as the feasibility in providing this integrated care

Robust velocity dispersion and binary population modeling of the ultra-faint dwarf galaxy Reticulum II

We apply a Bayesian method to model multi-epoch radial velocity measurements in the ultra-faint dwarf galaxy Reticulum II, fully accounting for the effects of binary orbital motion and systematic offsets between different spectroscopic datasets. We find that the binary fraction of Ret II is higher than 0.5 at the 90% confidence level, if the mean orbital period is assumed to be 30 years or longer. Despite this high binary fraction, we infer a best-fit intrinsic dispersion of 2.8$_{-1.2}^{+0.7}$ km/s, which is smaller than previous estimates, but still indicates Ret II is a dark-matter dominated galaxy. We likewise infer a $\lesssim$ 1% probability that Ret II's dispersion is due to binaries rather than dark matter, corresponding to the regime $M_{\odot}/L_{\odot} \lesssim$ 2. Our inference of a high close binary fraction in Ret II echoes previous results for the Segue 1 ultra-faint dwarf and is consistent with studies of Milky Way halo stars that indicate a high close binary fraction tends to exist in metal-poor environments.Comment: 9 pages, 5 figures, to be submitted to MNRA